Type of Copula      τ Global Type I                           PFS                             OS       Error Rate 1st Interim Final Analysis Type I Error 1st Interim Final Analysis Type I Error Type-I error rate   0.05 0.00042 0.02990 0.03 0.0014 0.01938 0.020 Independence 0 0.048 0.0004 0.0305 0.0307 0.0009 0.0176 0.0178 Normal 0.10 0.051 0.0008 0.0310 0.0318 0.0011 0.0199 0.0202   0.30 0.049 0.0005 0.0294 0.0295 0.0016 0.0211 0.0220   0.50 0.046 0.0003 0.0312 0.0315 0.0006 0.0194 0.0195   0.70 0.039 0.0002 0.0302 0.0304 0.0001 0.0188 0.0192 Frank 0.10 0.045 0.0004 0.0254 0.0258 0.0013 0.0192 0.0196   0.30 0.049 0.0006 0.0300 0.0306 0.0015 0.0188 0.0194   0.50 0.045 0.0002 0.0302 0.0304 0.0016 0.0184 0.0191   0.70 0.041 0.0001 0.0301 0.0302 0.0013 0.0176 0.0183 Gumbel 0.10 0.050 0.0005 0.0296 0.0301 0.0016 0.0192 0.0200   0.30 0.047 0.0017 0.0317 0.0324 0.0013 0.0170 0.0173   0.50 0.043 0.0005 0.0299 0.0304 0.0009 0.0178 0.0181   0.70 0.042 0.0005 0.0316 0.0321 0.0011 0.0184 0.0190

Table 5: Empirical global type I error rates, empirical significance level for each endpoint and proportion of not terminating the trial early using O'Brien-Fleming boundaries and assuming unequal allocation of the type I error rate of 0.03 for PFS and 0.02 for OS; results based on 10,000 simulations.